Synthesis Of Zeolite Beta Research Articles

Seeds-induced fluoride media synthesis of nanosized zeolite Beta crystals

This study reports on the seeded synthesis of zeolite Beta in fluoride media. Crystal growth kinetics of the material as a function of seed content, crystallization temperature and Si/Al ratio of the initial gel is studied. After the optimization of crystallization conditions a highly crystalline material with crystal size 100–300nm is synthesized. A counterpart zeolite Beta sample with similar characteristics is obtained in hydroxyl media. The physicochemical properties of fluoride and hydroxyl media syntheiszed zeolites are compared as particular attention is paid to the nature, number and distribution of their active sites. Zeolite Beta sample synthesized in fluoride media exhibits larger number of Broensted acid sites, while the concentration of Lewis acid sites is higher in the zeolite synthesized in hydroxyl media. The two materials are tested in m-xylene transformation, where zeolite Beta synthesized in fluoride medium shows superior performance. The set of experimental data unambiguously proves that seeded synthesis of zeolites in fluoride medium is a promising alternative of the conventional zeolite synthesis in hydroxyl medium.

Influence of TEA2O/SiO2 ratio on the polymorph formation and crystallization of zeolite beta

Zeolite beta is formed by different proportions of polymorphs. The influence of the syntheses conditions on the polymorphs formation has not been systematically studied up to now. In the present work a detailed study of the effect of the variation of TEA2O/SiO2 on the synthesis of zeolite beta has been carried out, for different molar ratios: 0.15, 0.27, 0.50 and 0.75. TEA2O concentration affects the crystallization kinetics, crystal size and morphology, polymorph proportion, textural properties and Al content in the final products. TEA2O/SiO2 = 0.27, seems to be a threshold value below or above which the nucleation rate decreases. For this ratio nanosize beta was obtained with the highest content of polymorph A, highest surface area and micropore volume. Lower or higher TEA2O/SiO2 ratios resulted in larger crystal size and higher content of polymorph B. The proportion of polymorphs obtained were in the range of 32%A–68%B to 51%A–49%B.

Synthesis of zeolite Beta, MFI, and MTW using imidazole, piperidine, and pyridine based quaternary ammonium salts as structure directing agents

The synthesis of zeolites is investigated using a variety of quaternary ammonium salts of imidazole, piperidine, and pyridine based structure directing agents. The materials were characterized by a complementary combination of X-ray diffraction, N2-adsorption/desorption, scanning electron microscopy, and transmission electron microscopy. Only suitable quaternary ammonium salts were able to form zeolites Beta, MFI, and MTW. Zeolites (especially Beta) obtained using these quaternary ammonium salts are nanocrystalline in nature and exhibited high surface area and pore volume compared to conventional zeolites. Experimental evidence and density functional theory studies suggest that a limited conformational freedom, provided by the cyclic structure of the quaternary ammonium salts, is an important prerequisite and acts as a structure directing agent for the synthesis of zeolites.

Synthesis of Dicationic Ionic Liquids and their Application in the Preparation of Hierarchical Zeolite Beta

Piperidine- and imidazole-based dicatoinic ionic liquids have been developed for the synthesis of zeolite Beta. Hierarchical Beta has a larger surface area and pore volume than conventional Beta. Beta derived from a dicationic ionic liquid exhibited remarkably higher catalytic activity than the conventional Beta. Experimental evidence and DFT calculations suggest that only a suitable conformation of such dicationic ionic liquids is able to form zeolite Beta (see scheme).

Nonionic emulsion-mediated synthesis of zeolite beta

Zeolite beta synthesis was first carried out in a newly developed emulsion system containing nonionic polyoxyethylated alkylphenol surfactant, which showed interesting non-conventional features. Compared to the conventional hydrothermal synthesis of zeolite beta, the reported nonionic emulsion system showed a faster nucleation rate. Furthermore, the emulsion system could stabilize the beta product and retarded its further transformation to ZSM-5 even under the high crystallization temperature at 453 K. Additionally, the beta particle size could be tuned by the adoption of different lengths of alkyl chain in the surfactant and cosurfactant. Control experiments showed each emulsion component played a crucial role in the zeolite beta growth. The approach proposed in this paper might be extended to apply for the syntheses of other types of zeolites with particle size under control.

Critical Factors in the Seed‐Assisted Synthesis of Zeolite Beta and “Green Beta” from OSDA‐Free Na+–Aluminosilicate Gels

Organic structure-directing agent (OSDA)-free synthesis of zeolite beta is a subject of both scientific and industrial interest. Herein, we report a comprehensive investigation into the effects of various parameters on the seed-assisted crystallization of zeolite beta in the absence of OSDA. The crystallization behavior of "OSDA-free beta" is strongly governed by the chemical composition of the starting Na(+)-aluminosilicate gel as well as by the Si/Al ratios of the calcined beta seed crystals, which are prepared using tetraethylammonium hydroxide (TEAOH). Furthermore, OSDA-free beta seed crystals can be used to form zeolite beta, termed "green beta". XRD, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy, and ²⁷Al magic angle spinning NMR analyses showed that the OSDA-free beta and green beta were of high purity and crystallinity. The nitrogen adsorption-desorption of OSDA-free beta and green beta revealed higher surface areas and larger volumes in the micropore region than those of the beta seeds synthesized with OSDA after calcination. These results provide a robust and reliable process for the environmentally friendly production of high-quality zeolite beta in a completely OSDA-free Na(+)-aluminosilicate system.

SYNTHESIS OF ZEOLITE BETA DIRECTLY FROM RICE HUSK ASH: EFFECT OF REACTION COMPOSITION ON CRYSTALLINITY OF ZEOLITE BETA

White rice husk ash obtained from complete uncontrolled burning of rice husk contains more than 94% silica. The ash, which consists of crystalline silica of the type tridymite and a-crystobalite, was used directly as a source of silica in the synthesis of zeolite beta. The mole oxide ratio of the initial gel of 1.25-8Na2O: 10-120SiO2: Al2O3: 1-20TEA2O: 150-1000H2O was prepared and heated at 150°C in a static condition for 6 d. The solid phases formed were monitored by XRD technique. Influence of reaction mixture ratio in the initial gel to the crystalline products formed was studied. Results showed that the pure zeolite beta was formed in a certain range of reaction mixture, i.e.: 1.25-4Na2O : 15-45SiO2 : Al2O3 : 4-10TEA2O : 240-480H2O. The other ratio of reaction mixtures produced crystalline phases such as analcime, Na-P, mordenite, and gismondine, and non-reacted of a-crystobalite and tridymite. Keywords: rice husk ash, tridymite, a-crystobalite, zeolite beta, synthesis

Synthesis of Zeolite Beta by the Vapour-Phase Transport Method Using Tetraethylammonium Bromide as the Organic Template

Abstract The synthesis of zeolite beta by the vapour-phase transport method using tetraethylammonium bromide (TEABr) as a cheap organic template was studied. With TEABr being solid state at room temperature, the materials were mixed directly, and the preparing xerogel was not necessary. The products were characterized using X-ray diffraction, scanning electron microscopy, and infrared spec-troscopy. The crystallization process of zeolite beta was investigated. The results indicated that zeolite beta can be synthesized when the ratio of n(SiO2)/n(Al2O3) was 15–200, n(NaOH)/n(Al2O3) was 0.35–0.55, and n(TEABr)/n(SiO2) was more than 0.12. The solvent of the synthesis system was a little, which just came from vapour. The concentrations of TEA+ and Na+ were high, and the crystallization speed was fast. At 423 K, the crystallization process was completed after 10 h. The alkalinity of the system has a very important impact on the crystallization process, affecting crystallization speed and particle size. Too long time and too high temperature were disadvantageous to the crystallization of zeolite beta. The zeolite beta synthesis followed the liquid phase synthesis mechanism. At the initial crystallization stage, the morphology of the products was ellipse, and at the last crystallization stage, the products were transformed into polyhedron. The particle sizes were mostly 0.3 μm and the distribution range of sizes was narrow. The vapour-phase transport method was more promising and economical than the traditional hydrothermal method, and it can simplify the synthetic process and reduce the cost.

Synthesis of zeolite beta with pretreated rice husk silica and its transformation to ZSM-12

Silica with 98% purity was prepared from rice husk by acid leaching and used as a silica source for the syntheses of zeolite beta (Beta) under hydrothermal conditions with gel Si/Al ratios of 8, 13, 15, 20, 50, 100, 150, and 200. Based on powder X-ray diffraction patterns, samples with gel Si/Al ratios of 8–20 contained only the pure phase of Beta and the highest relative crystallinity was observed in the Beta with gel Si/Al ratio of 13. This sample was further characterized by scanning electron microscopy, particle size analyzer and N 2 adsorption analysis. The Beta particles were sphere shaped with the average particle size of 1.5 μm and a surface area of 670 m 2 g −1. The samples with gel Si/Al ratios ranging from 50 to 200 showed mixed phases of Beta and ZSM-12, and the latter phase was more dominant as the Si/Al ratio increased.

Microwave-assisted hydrothermal synthesis of zeolite Beta coatings on ALD-modified borosilicate glass for application in microstructured reactors

Stable zeolite Beta coatings with a thickness of 1–2 μm were synthesized on a borosilicate glass substrate by microwave-assisted hydrothermal synthesis. Prior to the synthesis, surface roughness of the substrate was increased to 1.0 μm. Then, two thin films of zirconia and titania were successively deposited at 300 °C on the glass substrate by atomic layer deposition using ZrCl4 as metal precursors for zirconia and TiCl4 for titania, respectively. Oxygen and H2O were used as oxygen precursors in the ALD process. The internal zirconia film protects the glass substrate from dissolution in a highly alkaline synthesis solution. The outer titania film was made superhydrophilic (>15 OH/nm2) by an UV irradiation, which enhances the nucleation and crystallization processes on the substrate. The duration of the zeolite nucleation period was decreased by using the additive effect between fluoride ions and the zeolite seed solution under microwave irradiation. A uniform zeolite Beta coating was obtained already after 8 h at 150 °C in a microwave from a precursor gel with SiO2/Al2O3 = 25, TEAOH/Al2O3 = 8.75, H2O/SiO2 = 11.6, NH4F/SiO2 = 0.2. This is almost six times faster comparing to conventional hydrothermal synthesis.

Contribution to the hydrothermal synthesis of zeolite beta and its modifications with gallium

The zeolite beta is a crystalline synthetic aluminosilicate with wide-pore size (6 to 9 A) and a Si/Al ratio from 5 to 100. In this study, we have investigated the influence of several synthesis parameters on the physicochemical properties of the materials. The synthesis of zeolite beta has been performed by hydrothermal method, the aluminum source and gallium content in the structure being variable. The structural characterization was carried out by means of X-ray diffraction, SEM and 27Al and 71Ga MAS NMR spectroscopy. When the aluminum sulfate is used as aluminium source, zeolite beta with higher crystallinity is generated. All the samples showed a XRD pattern similar to crystalline zeolite beta and the 27Al and 71Ga MAS NMR spectrum demonstrated that the incorporation of both heteroatoms was efficient.

Compositional and kinetic studies on the crystallization of zeolite beta using cost-efficient TEABr without seed under static and stirred conditions

Zeolite beta was successively synthesized in the presence of TEABr as organic template within 36 h under static and stirred conditions at 423 K. In order to clearly demonstrate the effects of individual component and interaction between components on the crystallization of zeolite beta using TEABr, a ternary compositional diagram for TEABr, Al 2O 3 and Na 2O was drawn at constant SiO 2 and H 2O contents. There are mainly three compositional zones in which zeolites, beta, ZSM-5 and mordenite are formed. The results suggest that Na + cation should have acted as structure-directing agent as well as charge balancing for AlO 2 −, leading the crystallization toward the formation of mordenite or ZSM-5 depending on its content. The results clearly show that the crystallization toward pure zeolite beta becomes favorable at lower Al 2O 3 content. In addition, it is interesting to notice that Na 2O and Al 2O 3 contents would play key roles simultaneously in the crystallization toward the formation of pure zeolite beta. The results of thermal analysis show that TEA + ion also partially acts as charge-balancing agent depending on Al content, that is, it is more likely to interact with Si–O − rather than with Al–O − at lower Al content, thus resulting in the more decomposition of TEA + ions interacting with Si–O − at lower Al content in temperature range between 473 and 623 K. The kinetic study based on 3Na 2O–18TEABr–0.8Al 2O 3–25SiO 2–440H 2O was conducted at 413, 418 and 423 K, respectively, and the results suggest that as long as a correct crystallization temperature is applied to the synthesis of zeolite beta, the crystallization of zeolite beta does not seem to be so sensitive to temperature.

On the catalytic performance in isopropylation of benzene over H/β zeolite catalysts: Influence of binder

A largely unsolved problem in environmentally detrimental waste products is utilization of flyash. Zeolite beta is synthesized using flyash as a source of silica and alumina. Isopropylation of benzene has been used as a probe reaction to evaluate the quality of flyash-based zeolite beta. Influence of the different percentages of alumina binder and formulations on the catalytic performance in isopropylation of benzene reaction over protonic forms of flyash zeolite beta (H/β) has been investigated. It is also shown that, flyash based zeolite beta synthesis opens new possibilities for commercialization of environmentally detrimental product to cost-effective and eco-friendly catalyst of commercial interest.

Effect of agitation on the synthesis of zeolite beta and its synthesis mechanism in absence of alkali cations

Zeolite beta was hydrothermally synthesized in the TEAOH–SiO 2–Al(0)–H 2O system in the absence of alkali cations. The effects of agitation under various TEAOH/SiO 2 molar ratios on the crystallization kinetics, particle size, particle size distribution, and framework SiO 2/Al 2O 3 of synthesized zeolite beta were studied. The as-synthesis and calcinated zeolites were characterized by XRD, TEM, N 2 adsorption. The effect of the agitation on the induction time, the particle size, and the framework SiO 2/Al 2O 3 ratio of the synthesized zeolites was more pronounced at high TEAOH/SiO 2 molar ratio (0.6) than at a low TEAOH/SiO 2 molar ratio (0.21 and 0.4). Under agitation, the induction time, the particle size, and the framework SiO 2/Al 2O 3 molar ratio of the zeolite greatly decreased with the increase of the TEAOH/SiO 2 ratio. While under the static state, the minimum induction time and the crystal particle size existed at TEAOH/SiO 2 ratio = 0.4, and the framework SiO 2/Al 2O 3 molar ratio of the zeolite increased with the increase of TEAOH/SiO 2 ratio. The crystallization proceeded via solution phase nucleation mechanism.

Conversion of rice husk ash to zeolite beta

White rice husk ash (RHA), an agriculture waste containing crystalline tridymite and α-cristobalite, was used as a silica source for zeolite Beta synthesis. The crystallization of zeolite Beta from RHA at 150 °C in the presence of tetraethylammonium hydroxide was monitored by XRD, FTIR and 29Si MAS NMR techniques. It was found that zeolite Beta started to form after 12 h and the complete crystallization of zeolite Beta phase was achieved after 2 d. XRD, 29Si MAS NMR and solid yield studies indicate that the transformation mechanism of silica present in RHA to zeolite Beta involves dissolution of the ash, formation of an amorphous aluminosilicate after 6 h of crystallization, followed by dissolution in the mother liquor and final transformation to pure zeolite Beta crystals.

Solid state transformation of TEAOH-intercalated kanemite into zeolite beta (BEA)

The work reported herein involves the synthesis of zeolite beta by solid state transformation of TEAOH-intercalated kanemite, at 140 °C, under autogenous pressure. A series of TEAOH-intercalated kanemite samples were prepared by intercalation of kanemite with TEAOH at room temperature followed by centrifugation and drying at 35 °C for 24 h. The XRD, TG-DTA and chemical analyses of the TEAOH-intercalated kanemite samples revealed that either the TEAOH molecules were intercalated into the interlayer spaces or strongly adsorbed onto the outer surfaces of kanemite. Zeolite beta samples in high yields (71–97%) were obtained by solid state transformation of TEAOH-intercalated kanemite samples having moderate amounts of TEAOH (TEAOH/SiO2 = 0.11–0.23). The XRD measurements showed that the zeolite beta samples obtained from the present method were phase-pure and highly crystalline. SEM studies revealed that the zeolite beta samples were composed of agglomerated crystallites. For the zeolite beta samples, surface areas of as high as 586 m2 g−1 were observed by the BET method. In addition, the zeolite beta sample (SiO2/Al2O3 = 12) obtained from TEAOH-intercalated kanemite was found to be active for the cracking of n-hexane and its performance was comparable to a standard zeolite beta sample (SiO2/Al2O3 = 20).

Synthesis of zeolite beta in fluoride media under microwave irradiation

Zeolite beta has been successfully prepared at 150 °C within 4 h by direct synthesis under microwave irradiation. Addition of seeds into the synthesis solution under microwave irradiation did not affect overall synthesis time of the material significantly, while addition of ammonium fluoride accelerated the crystallization of zeolite beta. In particular, microwave technique combined with fluoride species and seeding led to more rapid synthesis of crystalline zeolite beta. Upon microwave irradiation fluoride species and the microwave-activated water in the synthesis solution might be ascribed to shortening an induction period at the nucleation step, resulting in the rapid synthesis of the material.

Influence of alkalinity on particle size distribution and crystalline structure in synthesis of zeolite beta

Influence of alkalinity (OH -/SiO 2) on particle size distribution and crystalline structure in synthesis of zeolite beta at a short crystallization period (60 h) has been studied. The results indicate that the highest crystallinity of synthetic zeolite beta at alkalinity of 0.24, 0.35 occurs when Al 2O 3·H 2O and NaAlO 2 are respectively used as aluminium sources. At an alkalinity higher than 0.39, zeolite beta can not be obtained when Al 2O 3·H 2O is used as aluminium source. The difference of particle sizes between zeolite beta synthesized from gels of different alkalinity is 0.7–0.8 μm. The widest particle size distribution of zeolite beta synthesized occurs when the alkalinity is 0.23–0.24. Along with the increase of the alkalinity, zeolite beta synthesized changes as follows: vibration peak of 1071 cm −1 by IR moves to a higher position, the framework Si/Al ratio determined by 29Si MAS NMR first increases gradually and then decreases, but the change of OhAl/TdAl ratio determined by 27Al MAS NMR is contrary to that of the framework of the Si/Al ratio. In addition, the Si(O −) site existing in the TEA-β is confirmed by NMR, and the mechanism of alkalinity influencing crystallization is discussed.

Characterization of Beta/MCM-41 composite molecular sieve compared with the mechanical mixture

A Beta/MCM-41 composite was prepared for the first time through a two-step crystallization process combining a low crystallized zeolite Beta synthesis gel with a surfactant cetyltrimethylammonium bromide (CTAB) solution. The composite has been investigated and compared with a mechanical mixture of Beta and MCM-41 for their structure, acidity and catalytic activity by means of XRD, SEM, 129Xe NMR, DTG, N2 adsorption, IR spectra of pyridine and catalytic cracking reaction. The XRD result shows that the Beta/MCM-41 composite possesses a well-ordered mesoporous MCM-41 phase and a zeolite Beta phase. The result of N2 adsorption indicates that the composite contains a bimodal mesopore system and the microporous structure of zeolite Beta. Moreover, the results of 129Xe NMR and DTG suggest that the mesopore wall of the composite is constructed by a lot of secondary building units characteristic of zeolite Beta, which is quite different from the amorphous character of MCM-41 in the mechanical mixture. Although the total number of acid sites of the composite is comparable to that of the mechanical mixture, the composite possesses more strong Brønsted acid sites due to the initially crystallized mesostructure and shows higher catalytic activity for n-heptane cracking compared with the mechanical mixture.

Ecology as a social and economic issue

A Beta/MCM-41 composite was prepared for the first time through a two-step crystallization process combining a low crystallized zeolite Beta synthesis gel with a surfactant cetyltrimethylammonium bromide (CTAB) solution. The composite has been investigated and compared with a mechanical mixture of Beta and MCM-41 for their structure, acidity and catalytic activity by means of XRD, SEM, 129Xe NMR, DTG, N2 adsorption, IR spectra of pyridine and catalytic cracking reaction. The XRD result shows that the Beta/MCM-41 composite possesses a well-ordered mesoporous MCM-41 phase and a zeolite Beta phase. The result of N2 adsorption indicates that the composite contains a bimodal mesopore system and the microporous structure of zeolite Beta. Moreover, the results of 129Xe NMR and DTG suggest that the mesopore wall of the composite is constructed by a lot of secondary building units characteristic of zeolite Beta, which is quite different from the amorphous character of MCM-41 in the mechanical mixture. Although the total number of acid sites of the composite is comparable to that of the mechanical mixture, the composite possesses more strong Brønsted acid sites due to the initially crystallized mesostructure and shows higher catalytic activity for n-heptane cracking compared with the mechanical mixture.